Core sampler

ABSTRACT

A core sampler, particularly for use in oil prospecting, including a flexible movable ring (5), provided in particular at the front end (2) of the core sampler, which end is connected to a coring bit (3), for grasping a core sample (C) to be brought to the surface. The ring has a cylindrical internal surface (6) to be clamped around the core sample (C), and a frustoconical external surface (7) tapering towards the front end (2). In the end or starting position, the ring (5) is exposed to zero or minimal strain from the bearing surface (12) and has an internal diameter no smaller than the outer diameter of the core sample (C) to be grasped. The core sampler (1) comprises control mechanism for longitudinally moving the movable ring (5) from the end starting position to an end clamping position. A flexible sleeve (15) is advantageously substantially coaxial with the movable ring (5) and engages the side thereof opposite the front end (2) of the core sampler (1).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a core sampler, particularly for use inoil prospecting, comprising, particularly at its front end associatedwith a coring bit, for grasping a core sample to be brought to thesurface:

a deformable moving ring having a cylindrical internal surface designedto clamp the core sample, particularly when the latter is made of aso-called consolidated substance, and a frustoconical external surfacewhich tapers toward the front end,

a cavity which has a wall with an internal cone frustum-shaped bearingsurface corresponding in terms of its shape and size to the externalfrustoconical surface of the moving ring, which is fixed to the coresampler at least in the longitudinal direction thereof and in which themoving ring can be housed in such a way that it can occupy, in thelongitudinal direction, two extreme positions, one being a clampingposition in which the moving ring pressed, on its small-diameter side,into the internal cone frustum is deformed inward so as to reduce itsinternal cross section and thereby clamp the core sample in order toimmobilize it at this point in the core sampler.

2. Background of the Prior Art

A significant drawback of a core sampler of this kind, known at thistime from patent application FR-A-2 088 255 (FIG. 1B) arises from thefact that the deformable moving ring is usually an elastic ring with afrustoconical external surface, split longitudinally and the insidediameter of which is smaller than the nominal inside diameter of thecore sampler or than the outside diameter of a core sample made ofconsolidated substance, cut by the core sampler. The core sample whichis formed has therefore to be pushed into the split ring in such a wayas to open up this ring and keep it open. Blockage, known to the personskilled in the art, of the core sample in the split ring, and thereforein the core sampler, can therefore occur as a result of the constantfriction between the core sample and the split ring and as a result, forexample, of core-sample debris which may move therein because of thisand become wedged between the core sample and the end of one of theslits if these slits are not made over the entire length of the ring. Anexpensive core-sampling operation may be completely compromised by thisblockage. What is more, in the case of an unconsolidated core sample(sand, etc.), this smaller inside diameter of the deformable ring slowsthe progress of the core sample and upsets the original arrangement ofits constituents, and this therefore considerably compromises theefficiency and results of the core-sampling.

Another significant drawback of the known core sampler arises from thecomplexity of producing a flattenable sheath as described in patentapplication FR-A-2 088 255, even an elastic one, because clearly, for agiven circumference that allows a cylindrical core sample (FIG. 1B) tobe housed, the sheath may have difficulty in adopting a flattenedposition where the largest transverse dimension is equal to twice thediameter of the aforementioned circumference. Furthermore, theflexibility imposed on the sheath means that the core sampler fluidsystem has to be kept under pressure while this sampler is being raised,and even for longer than this, until a complex handling operation, notexplained, has been performed, if the core sample is not to be disturbedover a significant part of its length starting at the point where thesheath was flattened.

In addition, the aforementioned document neither shows nor suggests anyinteraction between the split ring and the flattenable sheath.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome these drawbacks andto provide a core sampler whose operation is dependable, in the case ofa core sample made of a consolidated substance, thanks to the fact thata large enough passage is provided for this sample and possibly, in thecase of a core sample made of a substance that is undetermined at thestart, thanks to the presence of means capable of effectively graspingcore samples both made of consolidated and made of unconsolidatedsubstances.

To this end, according to the invention, provision is made that

in the other extreme position, known as the starting position, themoving ring is exposed to zero or minimal strain from the bearingsurface and has an inside diameter not smaller than the outside diameterof the core sample to be grasped, and

the core sampler comprises control means designed to move the movingring in the longitudinal direction from the extreme starting position asfar as the extreme clamping position.

According to a preferred embodiment of the invention which among otherthings makes it possible to avoid the other drawback mentionedhereinabove, the control means comprise

a deformable sleeve,

arranged so that it is approximately coaxial with the moving ring,bearing against the opposite side thereof to the side at the front endof the core sampler,

having an inside diameter not smaller than the outside diameter of thecore sample,

able to move in the aforementioned longitudinal direction, over a travelnot shorter than that of the moving ring between its two extremepositions, and

comprising a deformable cylindrical wall situated immediately around thecore sample to be grasped, and

means which can be controlled in order to deform the deformable wallinward by applying a force to it, so as at least to clamp the coresample in order to fix thereto.

It is then particularly advantageous, at least as far as its deformablewall is concerned, for the sleeve to be made of a ductile metal whichretains the deformation imposed on it.

Other details and particular features of the invention will emerge fromthe secondary claims and from the description of the drawings which areappended to this text and which, sometimes on different scales,illustrate, by way of nonlimiting examples, some embodiments of the coresampler of the invention.

FIG. 1 depicts diagrammatically, with cutaway and in longitudinalsection, a first embodiment of a core sampler of the invention.

FIG. 2 depicts diagrammatically, with cutaway and in longitudinalsection, a second embodiment of a core sampler of the invention.

FIG. 3 depicts in longitudinal section a deformable sleeve used in thecase of the second embodiment of the invention.

FIG. 4 shows diagrammatically in cross section a type of deformation, atits most deformed point, of a deformable sleeve, the starting section ofwhich is depicted in broken line.

FIG. 5 shows diagrammatically in longitudinal section the same type ofdeformation of the deformable sleeve, the starting shape of which isdepicted in broken line.

FIG. 6 shows diagrammatically in longitudinal section another type ofdeformation of the deformable sleeve, the starting shape of which isdepicted in broken line.

FIG. 7 depicts diagrammatically, in longitudinal section, with cutaway,the core sampler of FIG. 1 or 2 at the point of connection of the innerand outer barrels it comprises.

FIG. 8 depicts diagrammatically, with cutaway and in longitudinalsection, a third embodiment of a core sampler of the invention.

FIG. 9 depicts diagrammatically in longitudinal section, with cutaway,the core sampler of FIG. 4 at the point of connection of the coaxialbarrels it comprises.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the various figures, the same reference notation denotes elementsthat are identical or analogous.

With a view to grasping a core Sample (not depicted) to bring back tothe surface, the core sampler 1 of the invention (FIG. 1) comprises,particularly at its front end 2 associated with a coring bit 3 carriedby an outer barrel 4, a deformable moving ring 5 which has

a cylindrical internal surface 6 designed to clamp the core sample C ina known way, particularly when this core sample is made of a so-calledconsolidated substance, and

a frustoconical external surface 7 which tapers toward the front end 2.

The core sampler 1 also comprises a cavity 8 which, for example, formspart of a known inner barrel 9 via which it is fixed to the core sampler1, at least in the longitudinal direction thereof. The cavity 8 has, forthe moving ring 5, a wall with a bearing surface 12 in the shape of aninternal cone frustum corresponding, in the known way, in terms of itsshape and size to the aforementioned external frustoconical surface 7.The moving ring 5 can be housed in the cavity 8 in such a way that itcan occupy two extreme positions therein, in the longitudinal direction.One extreme position is the clamping position in which the moving ring 5pressed, following a movement in the longitudinal direction toward thesmall-diameter side 13, into the internal cone frustum 12 is deformedinward so as to reduce its internal cross section and in which itthereby clamps the core sample C in order to immobilize it at this pointin the core sampler 1.

The term deformable may be understood as meaning that the moving ring 5can, for example, be "crumpled" so as to reduce its internal crosssection following radial pressure inward, exerted on its externalfrustoconical surface, or alternatively that it is, for example, slitthrough its entire thickness and over at least a significant part of itslength (FIG. 2) or its entire length (FIG. 1) so that its internal crosssection can be reduced under the same conditions of an aforementionedradial pressure.

In place of a cone frustum or of a frustoconical surface, it is possiblealso to use a pyramid frustum, or a cone frustum and a pyramid frustummay also be combined.

The so-called cylindrical internal surface and/or the so-calledfrustoconical external surface may be formed, for example, by folds ofendless tape arranged in the manner of a so-called star-shaped filtercanister as used, for example, in the automotive industry.

According to the invention, in the other extreme position, known as thestarting position, the moving ring 5 is exposed to zero or minimumstrain from the internal frustoconical wall 12 and therefore has aninside diameter not smaller than the outside diameter of the core sampleC to be grasped.

Also according to the invention, the core sampler 1 comprises controlmeans designed to move the moving ring 5 in the longitudinal directionfrom the extreme starting position as far as the extreme position ofclamping the core sample.

In one embodiment (not depicted) of the core sampler 1, these controlmeans may be an annular piston connected to the moving ring 5, placedbetween the inner barrel 9 and outer barrel 4 and actuated for exampleby a pressure of the core-sampling fluid which is greatly increased, inways known by those skilled in the art, at the end of core-sampling justbefore the core sample starts to be raised.

According to an advantageous embodiment of the invention (FIGS. 1 and2), the control means may comprise a deformable sleeve 15 which isarranged so that it is approximately coaxial with the moving ring 5,bearing against the opposite side thereof to the side facing the frontend 2. The deformable sleeve 15 has an inside diameter not smaller thanthe outside diameter of the core sample C and it can move in theaforementioned longitudinal direction, over a travel not shorter thanthat of the moving ring 5 between its two extreme positions. Thedeformable sleeve 15 additionally comprises a deformable cylindricalwall 16 situated immediately around the core sample C to be grasped. Theaforementioned control means further comprise means which can becontrolled in order to deform the deformable wall 16 inward by applyinga force, preferably at several points distributed around the coresample, so as at least to clamp this sample in order to fix solidlythereto if the core sample C is made of a consolidated substance.

As the core sample C may be made of an unconsolidated substance, atleast at the point where the deformable sleeve 15 clamps it, thedeformable wall 16 of this sleeve may then be made of a material chosenso that it can in practice be stretched toward the inside of thedeformable sleeve 15, starting from a point or preferably several pointssituated practically in at least one and the same transverse plane,these points moving closer together and forming a restriction whichimpedes the passage of unconsolidated substance, then held captive inthe inner barrel 9 of the core sampler 1. The thickness of the wall 16is chosen as a function of the force to be applied and it may vary as afunction of preferred points for deformation.

At least in the case of unconsolidated substances, it is preferablethat, at least as far as its deformable wall 16 is concerned, thedeformable sleeve 15 should be made of a ductile material which retainsthe deformation it has received, for example made of a metal or metallicalloy which in practice is inelastic.

The sleeve 15 of the invention may also be made of one or more materialsthen combined in various ways. Among other things, if it is desired thatno passages or fissures should occur as a result of deformation, thesleeve 15 may be metallic and comprise, at least over part of itsexternal peripheral surface, for example the surface most exposed tocracking, a jacket made of an elastic material (for example made ofrubber vulcanized on to the sleeve 15) which remains appreciablyimpervious to a passage of fluid that deforms the sleeve 15.

The aforementioned sleeves 15 may have a rough internal surface so thatthey catch on the core sample more effectively.

The aforementioned control means may comprise an annular chamber 17situated approximately coaxially around the deformable sleeve 15, thedeformable wall 16 of which may form one wall of the chamber 17 on thesame side as the core sample C. Another wall of the chamber 17, parallelto the aforementioned wall, may be the inner barrel 9 and the chamber 17may be closed at its ends by thickened parts of the deformable wall 16and by O-ring seals which provide a seal between these parts and theinner barrel 9.

The chamber 17 is intended to receive a control fluid. A conduit 18 isprovided for supplying the control fluid to the annular chamber 17.Adjusting means known to those skilled in the art are provided forbringing the pressure of the control fluid to at least a pressure beyondwhich the deformable wall 16 deforms in order to at least bear againstthe core sample C.

Said control fluid may be the usual core-sampling fluid originating froma known installation on the surface. The conduit 18 may be formed, overat least part of its length, by an intermediate space or annularlongitudinal duct 19 between two, for example coaxial, barrels of thecore sampler 1, which barrels are arranged one inside the other like theinner barrel 9 in the outer barrel 4. The longitudinal duct 19 is thenin fluid communication with the annular chamber 17 via one or morepassages 20 through the inner barrel 9. At the front end 2, thelongitudinal duct 23 may also be in fluid communication (FIG. 1 or 2)with known nozzles 24 arranged in the coring bit 3, via a ring 25, alsoknown, for adjusting the pressure drop.

FIGS. 4 to 6 show, for a fragile core-sample substance, types ofdeformation of the deformable wall 16 that can be influenced by makinglines of weakness beforehand at points and in orientations that theperson skilled in the art will determine experimentally, in order toobtain, for example, a tight restriction of the passage cross section inthe deformed sleeve 15.

FIG. 7 shows by way of example, at the point 21 of connection of theinner barrel 9 and of the outer barrel 4 by a thrust ball bearing 22, aconduit 23 for supplying core-sampling fluid originating from aninstallation at the surface. The supply conduit 23 is in fluidcommunication with the annular longitudinal duct 19 between the outerbarrel 4 and inner barrel 9.

When, following a core-sampling operation, there is a desire to raisethe core sample C, the first operation is that of increasing, forexample, the flow rate of core-sampling fluid which comes from thesupply conduit 23 and escapes via the nozzles 24. The pressure of thecore-sampling fluid increases in the longitudinal duct 19 as a result ofthe pressure drop brought about by the adjusting ring 25 situateddownstream of the passages 20 in the direction of flow of the fluid.Beyond a pressure threshold which depends among other things on thematerial and on the thickness of the deformable wall 16, the pressure inthe annular chamber 17 causes one or more deformations of the deformablewall 16 which therefore clamps the core sample C and may fix solidlythereto if the core sample is made of a consolidated substance. At thisinstant, the core sampler 1 can be raised and the core sample C, eitherbecause it is still fixed to the bottom or on account of its weight,even though it is detached from the bottom, forces the deformable sleeve15 to bear against the deformable ring 5 and drive the latter into thecavity 8 with frustoconical walls 12. Because the surfaces arefrustoconical, this driving movement causes the deformable ring 5 to beclamped on the periphery of the core sample C and the latter thereby tobe immobilized at the base of the core sampler 1 for raising it.

If the substance of the core sample is not consolidated at the point ofthe deformable wall 16, this wall may be deformed, by the pressureapplied, to the extent that it restricts the passage in the inner barrel9 at this point enough to prevent the substance of the core sample fromescaping. Thus, during raising, the weight of the core sample pressingon the deformable sleeve 15 will, in this case also, force thedeformable ring into the cavity 8. At this instant, either thedeformable ring 5 tightens on to a consolidated or resistant-enough partof the core sample C and this part acts like a stopper, or the substanceof the core sample at the point of the deformable ring 5 is notresistant and escapes gradually as the ring 5 tightens, until the ring 5reaches the stop. For this, for example, the ring 5 may be splitlongitudinally (FIG. 1) and the lips 28 of the slit press together andthis prevents the ring 5 from being driven in any further. In this case,the aforementioned restriction is enough to close the inner barrel 9 atthe front end 2.

Two semi-cylindrical shells 30 may be arranged in the annular chamber 17in order to prevent deformation of the deformable wall 16 toward theinside of this chamber 17 under the action, for example, of debris fromthe core sample C passing between this sample and the deformable wall16.

The deformable ring 5 may bear on the core sample via generatrices ofits internal surface 6. This surface may be lined with a catchingmaterial or be knurled, or may have a catching net, etc.

As FIGS. 2 and 3 show, the deformable moving ring 5 and the deformablesleeve 15 may be merely one component, because they are either fixedtogether or made this way. In the latter instance, the part thatconstitutes the deformable ring 5 may be formed of several tabs 31 ofwedge-shaped longitudinal section and have slits between them so thatthey can tighten around a core sample C. The tabs 31 may, for example,have point contacts or contact along generatrices with the core sampleand/or with the internal cone frustum 12. They may also be covered ormachined as explained hereinabove in the case of the internal surface 6.A circular groove 32 may be provided at the point of connection of thetabs 31 and of the deformable sleeve 15, so as to make it easier for thetabs 31 to flex as they are driven into the cavity 8, toward the smalldiameter thereof.

According to FIG. 7, the inner barrel 9 may comprise, among otherthings, at its opposite end to the front end 2, a known valve 33allowing core-sampling fluid to leave the inner barrel 9 as the coresample C enters it.

According to another embodiment of the invention (FIGS. 8 and 9), theaforementioned means of adjusting the pressure may comprise, in theconduit 18 designed to supply the core-sampling fluid to the front end2, two lengths of ducting 37, 38 in parallel for the fluid. Each lengthof ducting 37, 38 may exhibit a given pressure drop for a given fluidflow rate. One of the lengths of ducting 37 is then arranged in such away that it can be closed by a controlled valve 39, for example by aball 39 thrown on to a valve seat 40 at the desired moment. The pressuredrop in the other length of ducting 38 is chosen to then bring about, atthe given fluid flow rate, an increase in pressure at least up to thepressure value which deforms the deformable wall 16 in the desired way.

The two lengths of ducting 37, 38 may advantageously be formed, at leastin part, in the case of each of them, by an annular space lying betweenthree approximately coaxial barrels of the core sampler 1. It istherefore preferable that a middle barrel 41 be arranged between theouter barrel 4 and the inner barrel 9. The annular space between theouter barrel 4 and the middle barrel 41 is the length of ducting 37, andthe one between the middle barrel 41 and the inner barrel 9 is thelength of ducting 38. The latter is in direct fluid communication withthe passage or passages 20 and possibly with channels 42 for the passageof fluid between the middle barrel 41 and inner barrel 9 at the frontend 2, while the ducting 37 is in direct fluid communication with thenozzles 24.

Another valve 43 (FIG. 9) in the form of a ball is arranged in a chamber44 which is in direct fluid communication with the ducting 38 and withthe supply conduit 23 and in fluid communication, controlled by theother valve 43, with the inside of the inner barrel 9.

During a core-sampling operation, provided the core sample enters theinner barrel 9, fluid can escape therefrom through a passage 45, throughthe other valve 43, through the chamber 44, through passages 49 to theducting 38 and through the channels 42 toward the bottom of thecore-sampling hole. Should this circuit become blocked, the fluid canstill escape toward one or more passages 46, another chamber 47 (for thevalve 39 at this moment absent), one or more passages 48 in order toreach the ducting 37 and therefore the nozzles 24.

Through the action of the other valve 43, fluid cannot travel from thesupply conduit 23 into the inner barrel 9. At the same time,core-sampling fluid can travel from the supply conduit 23 to the nozzles24 via the passage or passages 48 and the ducting 37.

At the end of core-sampling, before raising the core sampler 1, all thatis required is for the ball 39 to be sent into the conduit 23. It ispushed into this conduit by the fluid until it comes to rest on its seat40 and it then closes the entry to the passages 48 and thereforepractically any flow rate of fluid through the nozzles 24. Given thatthe fluid from the supply conduit 23 can, from this moment on, pass onlythrough the passages 46, the chamber 44 and the passages 49 toward theducting 38 and therefore toward the passage channels 42, the fluidpressure increases and, via the passages 20, the fluid deforms thedeformable wall 16. The subsequent operations of raising the core sampleare as already described hereinabove.

It must be understood that the invention is not in any way restricted tothe embodiments described and that many modifications may be madethereto without departing from the scope of the present invention.

Thus, all of the deformable moving ring 5, the aforementioned means ofcontrolling it and the cavity may be arranged at other points along thecore sampler 1 than at its front end 2.

In addition, the ducting 37, 38 may be produced in some way other thanby the aforementioned corresponding annular spaces 37, 38.

List of Reference Numerals

C Core sample

1 Core sampler

2 Front end of core sampler 1

3 Coring bit

4 Outer barrel

5 Deformable moving ring

6 Ccylindrical internal surface of 5

7 Frustoconical external surface of 5

8 Cavity

9 Inner barrel

12 --Wall

Bearing surface

Internal cone frustum

Internal frustoconical wall

13 Small-diameter side of 12

15 Deformable sleeve

16 Deformable cylindrical wall

17 Annular chamber

18 Conduit

19 --Intermediate space

Annular longitudinal duct

20 Passages

21 Point of connection

22 Thrust ball bearing

23 Fluid supply conduit

24 Nozzles

25 Ring for adjusting pressure drop

28 Lips of split deformable ring 5

30 Semi-cylindrical shells

31 Tabs

32 Circular groove

33 Valve

37 --Ducting

Annular space

38 --Ducting

Annular space

39 --Controlled valve

Ball

40 Seat of valve 39

41 Middle barrel

42 Passage channels

43 Other valve (ball)

44 Valve chamber

45 Passage

46 Passage(s)

47 Other chamber, for valve 39

48 Passage(s)

49 Passages

What is claimed is:
 1. Core sampler associated with a coring bit (3),for grasping a core sample (C) to be brought to the surface:a deformablemoving ring (5) having a cylindrical internal surface (6) designed toclamp the core sample (C) and a frustoconical external surface, a cavity(8) which has a wall (12) with an internal cone frustum-shaped bearingsurface (12) corresponding in terms of its shape and size to theexternal frustoconical surface (7) of the moving ring (5), which isfixed to the core sampler (1) at least in the longitudinal directionthereof and in which the moving ring (5) can be housed in such a waythat it can occupy, in the longitudinal direction, two extremepositions, one being a clamping position in which the moving ring (5)pressed into the internal cone frustum (12) is deformed inward so as toreduce its internal cross-section and thereby clamp the core sample (C)in order to immobilize it at this point in the core sampler(1),characterized in that in the other extreme position, known as thestarting position, the moving ring (5) is exposed to zero or minimalstrain from the bearing surface (12) and has an inside diameter notsmaller than the outside diameter of the core sample (C) to be grasped,and the core sampler (1) comprises control means intended to move themoving ring (5) in the longitudinal direction from the extreme startingposition as far as the extreme clamping position.
 2. Core sampleraccording to claim 1, characterized in that the control means compriseadeformable sleeve (15),arranged so that it is approximately coaxial withthe moving ring (5), having an inside diameter not smaller than theoutside diameter of the core sample (C), able to move in theaforementioned longitudinal direction, over a travel not shorter thanthat of the moving ring (5) between its two extreme positions,comprising a deformable cylindrical wall (16) situated immediatelyaround the core sample (C) to be grasped, and means which can becontrolled in order to deform the deformable wall (16) inward byapplying a force so as at least to clamp the core sample.
 3. Coresampler according to claim 2, characterized in that the deformable wall(16) of this sleeve is made of a material chosen so that it can inpractice be stretched toward the inside of the sleeve (15), startingfrom one or more points along this sleeve which are therefore situatedapproximately in at least one and the same transverse plane, thesepoints moving closer together and forming a restriction which impedesthe passage of core sample substance.
 4. Core sampler according to anyone of claims 1 to 3, characterized in that the moving ring (5) is fixedto a deformable sleeve (15).
 5. Core sampler according to any one ofclaims 2 to 3, characterized in that the aforementioned control meanscomprisean annular chamber (17) which is situated approximatelycoaxially around the deformable sleeve (15), the deformable wall (16) ofthe sleeve forming one wall of the chamber (17) on the same side as thecore sample (C), and which is intended to receive a control fluid, aconduit (18) designed to supply control fluid to the annular chamber(17), and adjusting means for bringing the pressure of the control fluidto at least a pressure value beyond which the deformable wall (16)deforms in order to bear against the core sample (C).
 6. Core sampleraccording to claim 5, characterized in that the aforementioned controlfluid is the core-sampling fluid.
 7. Core sampler according to claim 5,characterized in that the conduit (18) is formed, over at least part ofits length, by an intermediate space (19, 38) between two barrels (4, 9;41, 9) of the core sampler (1), one barrel being arranged inside theother barrel.
 8. Core sampler according to claim 5, characterized inthat the adjusting means comprise, in the conduit (18) designed tosupply the core-sampling fluid to a front end (2) of the core sampler,at least two parallel lengths of ducting (37, 38) for the fluid, eachlength of ducting (37, 38) exhibiting a given pressure drop for a givenfluid flow rate, one of the two lengths of ducting (37) being arrangedin such a way that it can be closed by a controlled valve (39), thepressure drop in the other length of ducting (38) being chosen to thenbring about, at the given fluid flow rate, an increase in pressure. 9.Core sampler according to claim 8, characterized in that the two lengthsof fluid ducting consist, at least in part, of two annular spaces (37,38) lying between three coaxial barrels (4, 9, 41) of the core sampler(1), the outer barrel (4) and the inner barrel (9) and a middle barrel(41) placed between these three coaxial barrels, it be possible for theinner barrel (9) then to form for the annular chamber (17) a wallcoaxial with the deformable wall (16) and at least one passage (20)being pierced in the inner barrel (9) in order to place the annularchamber (17) and the annular space (38) between the inner barrel (9) andmiddle barrel (41) in fluid communication, and in that the valve (39) isthen situated in the length of ducting (37) formed by the annular space(37) between the outer barrel (4) and (41) in fluid communication withnozzles (24) of the coring bit (3).
 10. Core sampler according to anyone of claims 2 to 3, characterized in that said deformable wall (16) ismade of a ductile metal which retains the deformation imposed on it. 11.A core sampler for grasping a core sample, comprising:a coring bitassociated with said core sampler; a deformable moving ring having aninternal surface designed to clamp said core sample; a frustoconicalexternal surface on said moving ring; a wall defining a cavity having aninternal cone frustum-shaped bearing surface corresponding in shape andsize to said frustoconical external surface on said moving ring, saidmoving ring being housed in said cavity and being movable between afirst extreme position and a second extreme position within said cavity,and wherein said second position comprises a clamping position in whichsaid moving ring is pressed into said internal bearing surface anddeformed inwardly to clamp said core sample and said first positioncomprises a starting position wherein said moving ring is exposed tominimal strain from said internal bearing surface and has an insidediameter not smaller than the outside diameter of said core sample; anda control mechanism for moving said ring from said first extremeposition to said second extreme position.
 12. A core sampler accordingto claim 11, characterized in that said control means comprises adeformable sleeve.
 13. A core sampler according to a claim 12,characterized in that said deformable sleeve is deformable to form arestriction which impedes the passage of core sample substance.
 14. Acore sampler according to claim 12, characterized in that said movingring is fixed to said deformable sleeve.
 15. A core sampler according toclaim 12, characterized in that said control means further comprises anannular chamber for receiving a control fluid, said annular chambersituated approximately coaxially around said deformable sleeve;andadjusting means for bringing the pressure of said control fluid to atleast a pressure value beyond which said deformable sleeve deforms inorder to bear against said core sample.
 16. A core sampler according toclaim 15, characterized in that said control fluid comprises a coresampling fluid employed in cutting said core sample.
 17. A core sampleraccording to a claim 15, further comprising a conduit for conductingsaid fluid to said annular chamber.
 18. A core sampler according toclaim 15 wherein said adjusting means further comprises fluid flow rateresponsive passages for raising the pressure in said annular chamber.19. A core sampler according to claim 18 wherein said fluid communicatesthrough said core sampler with nozzles of said coring bit.
 20. A coresampler according to claim 12 wherein said sleeve is made of a ductilemetal that retains the deformation imposed on it.